The real minimum hourly cost of employment is £9.66 when additional costs such as pensions and National Insurance contributions are taken into account, according to data released by the Scottish Grocers Federation.

The data was gathered from a sample of retailers across Scotland and analysed by the University of Stirling’s Institute for Retail Studies.

It found that the real hourly cost of employment is 29% higher than the current National Living Wage rate of £7.50 per hour for staff aged 25 and over.

Professor Leigh Sparks of the University of Stirling said the true cost of employment was “being underestimated”.

“The independent convenience store sector is a vital component of community, economy and society across the country. Employing large numbers of local people such stores are vulnerable to rising costs, some of which are often unclear,” he said. “Rises in national minimum wage levels have knock-on impacts on the staff costs of almost 30%.”

Pete Cheema, SGF chief executive, said: “For the first time we have clear evidence of the real impact of rising staff costs on convenience retailers in Scotland. As small businesses, which play a vital part in the local economy, it is very difficult for stores to absorb these costs. This year more than 30% of stores have had to cut staff number with rising staff costs being the main reason given for this.

“Shop owners themselves are having to work longer; with 21% working more than 70 hours per week. We need the UK government to abandon the politically set target for increases in the national living wage. if, as expected, the national living wage rises to £7.90 next year, our members will face a real cost per hour of £10.17, this is not sustainable.”

The SGF has sent its data directly to the Low Pay Commission.